What is the greatest common factor of $12$ and $40$ ? Another way to say this is: $\operatorname{gcf}(12, 40) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $12$ and $40$ The factors of $12$ are $1$ $2$ $3$ $4$ $6$ , and $12$ The factors of $40$ are $1$ $2$ $4$ $5$ $8$ $10$ $20$ , and $40$ Thus, the greatest common factor of $12$ and $40$ is $4$. $\operatorname{gcf}(12, 40) = 4$